1. Field of the Invention
The present invention relates to an image forming apparatus and an image stabilization processing method, which are capable of forming monochrome or color images using an electrophotographic printing method, and more particularly to an image forming apparatus and an image stabilization processing method, which are applicable to copying machines, printers, facsimile machines, and multi-function machines provided with a copying function, a printing function, and a facsimile function.
2. Description of the Related Art
Conventionally, color copying machines and color printers (color machines) installed in company offices and the like, for printing out color documents have been potentially in great demand, but the machine prices and running costs thereof are so high that they cannot be readily or freely used like monochrome copying machines or monochrome printers (monochrome machines). This is also because most business documents are printed out in monochrome and therefore the demand for color printing of business documents has been low, so that there have been few color copying machines and color printers which are provided by manufacturers at low machine prices and with low running costs, and yet profitable enough for the manufacturers in spite of the low user demand for color printing output.
However, in recent years, there have been developed color copying machines and color printers for office use which have realized substantially the same machine prices and running costs as those of the monochrome machines and therefore permit users to feel free to carry out color printout in offices, thereby promoting a shift to color printing. With this development, color machines are replacing conventional monochrome machines in offices.
Under the circumstances, a technique has been proposed in which calibration processing for density correction is executed on four color toner images necessary for color image formation, when the power of the color machine is turned on (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2003-167394).
On the other hand, a control method for multi-function machines has been also proposed in which upon power-on of the machine, if the initial setup screen has been set to a facsimile mode screen, an image stabilization process for correction of image processing parameters is not executed but executed after printing is performed (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2002-44309). This control method is based on the concept that even with multi-function machines, facsimile printing is generally carried out in monochrome, and therefore image quality is not particularly affected even if the image stabilization process is not executed immediately after the start of the machine, which is initially set to a facsimile mode.
However, in the case of color machines including the color machine described above, calibration processing for density correction needs to be executed on the four color toner images necessary for color image formation. In general, the calibration processing is often executed immediately after power-on as described in Japanese Laid-Open Patent Publication (Kokai) No. 2003-167394. For this reason, adjustment time immediately after power-on becomes much longer in color machines than in monochrome machines. In addition, the color machines make preparations for color output even when only monochrome output is intended to be used, so that users are kept waiting due to adjustment for unnecessary color output.
Further, when color machines employ a two-component developing method using toner and carrier, toner density markedly changes depending on the environment. For this reason, immediately after the first power-on in the morning, or immediately after return from a power-saving mode, when environmental changes are most likely to occur, a plurality of processes, such as toner density measurement and density gradation correction, are necessitated, which tends to increase time required for processing executed during a wait.
The control method described in Japanese Laid-Open Patent Publication (Kokai) No. 2002-44309 has been proposed as a solution to the problem that adjustment time immediately after power-on is longer in color machines than in monochrome machines.
In this case, however, even if the initial setup screen has been set to the facsimile mode screen, and facsimile printing is to be performed in monochrome, when the environment has largely changed after the previous image stabilization process, degradation of image quality can occur, which necessitates resetting of image processing parameters. Further, a user can switch the facsimile mode screen to the copy mode screen for color printout, and hence color printout can be performed without execution of the image stabilization process. In such a case, image quality cannot be ensured.